1. FIELD OF THE INVENTION
The present invention relates to a method for producing an image. More particularly, it relates to a method for producing a heat resistant, high contrast image having high resolving power using a photographic material which comprises a support having thereon at least one silver halide emulsion layer, either directly or on at least one subbing layer on the support. It also relates to a method for easily producing a durable photomask having high resolving power and good edge sharpness using a photographic material which comprises a support having a masking layer thereon, the masking layer having thereon at least one silver halide emulsion layer, either directly or on at least one subbing layer on the masking layer.
2. DESCRIPTION OF THE PRIOR ART
The optical density of a silver image formed in the emulsion layer of a photographic material which comprises a silver halide emulsion layer on a support by exposing and developing the photographic material gradually decreases from a maximum value to a background value at the edge of the silver image. The spacing between the maximum image density portion and the background is usually about 1 micron. Therefore, it is difficult to obtain a high contrast silver image having closely separated lines (about 1 micron) or spacings. Silver grains existing between adjacent image lines reduce the image contrast and resolving power.
Moreover, since such an emulsion layer is colored due to thermal decomposition of the binder when heated to about 150.degree. to 200.degree. C., it cannot be used for purposes requiring heat resistance.
One field which requires a heat resistant image is "super-microphotography". An image reduced on a 35 mm film from a 9 by 14 inch (23 by 36 cm) size original with a reduction ratio of about 10 is usually called a "microphotograph," and an image further reduced (about 2.times.3 mm) by a factor of about 10 is called a "super-microphotograph." A microphotograph can thus be considered to be an image reduced by a factor of about 10 and a super-microphotograph an image reduced by a factor of about 100.
Since the image size of a super-microphotograph is about 2 by 3 mm or smaller, the enlarging factor is about 100 (10,000 based on area ratio) when a super-microphotograph is projected on a screen to provide the original image size. Consequently, a light intensity of about 10 million lux is necessary on the image surface of the super-microphotograph if the image projected on a transmission type screen, e.g., with a blackened back surface, is to have a light intensity of 100 lux when the screen has a transmission optical density of 1. In fact, the super-microphotograph is illuminated with a light intensity of about 12 to 13 million lux to compensate for the loss of the projection lens. The temperature of the emulsion layer of the super-microphotograph increases to several hundred degrees C., due to the heat generated by the light absorbed by the emulsion layer, when it is continuously illuminated with such a strong light. As a result, the binder of the emulsion layer is thermally decomposed and colored to cause the image projected on the screen to be dim and colored. Since the silver image areas absorb light well, the temperature of these areas preferentially increases and the binder of these areas is preferentially decomposed, whereafter the decomposition spreads into the surrounding areas. Decomposition of the binder in even the non-silver image areas proceeds in an accelerated easily damaged, that is, durability is poor. On the other hand, a hard mask is quite durable, but the production thereof is complicated. Also, the production of a hard mask requires a photoetching process that uses a photoresist which has low sensitivity and requires long exposure times.